Changing typesetting language without command

Question

I have a problem with typesetting LaTeX using both Greek and English characters. All this time, I've been using the polyglossia+fontspec packages which allowed me to change between Greek and English just by changing language on my keyboard.

This combination allows me to choose the fonts that I will use, but when letters in math mode mix with letters outside of math mode, the result is not so aesthetic. A solution to this is to substitute all math mode letter with \textrm, but I hope to find something less tiresome.

I actually want to change the font that I am using to, say, Kerkis. What I found online is that I have to add the following two packages

\usepackage{kmath,kerkis}
\usepackage[T1]{fontenc}

Adding these two packages (while removing fontspec) makes the file to not even compile.

So, my question is: how can I change the typesetting font in and out of math mode (let's say to Kerkis) while keeping the ability to change language without having to use a TeX command?

Edit: I used the mathspec package instead of fontspec, downloaded Kerkis fonts and manually added them using these:

\usepackage[MnSymbol]{mathspec}
\setmainfont{KerkisSans}
\setmathsfont(Digits,Latin)[Scale=MatchLowercase]{Kerkis}
\setmathsfont(Greek)[Scale=MatchLowercase]{Kerkis}
\usepackage{polyglossia}

Still, it feels like a half-measure since I'm feeling like I should just load a "Kerkis" package or something that would do the job for me, shouldn't I?

Answer 1

Here is the solution I suggested in the comment above:

\documentclass[11pt,oneside]{article}    
\usepackage{amsmath}
\usepackage{mathspec}%[MnSymbol]{mathspec} %<-No need for this in this example
%\usepackage{MnSymbol}
\defaultfontfeatures{Ligatures=TeX}
\setallmainfonts{Linux Libertine O}
\usepackage{polyglossia}
\setmainlanguage{greek}
\setotherlanguage{english}
\setmainfont{Linux Libertine O}
%\newfontfamily\greekfont{Linux Libertine O}

% Definitions of Greek (in math mode)
\def\alpha{α}
\def\beta{β}
\let\oldgamma\gamma %<-see the difference below
\def\gamma{γ}
\def\delta{δ}
\def\epsilon{ε}
\def\zeta{ζ}
\def\eta{η}
\def\theta{θ}
\def\iota{ι}
\def\kappa{κ}
\def\lambda{λ}
\def\mu{μ}
\def\nu{ν}
\def\xi{ξ}
%\def\ο{o}
\def\pi{π}
\def\rho{ρ}
\def\sigma{σ}
\def\tau{τ}
\def\upsilon{υ}
\def\phi{φ}
\def\varphi{ϕ}
\def\chi{χ}
\def\psi{ψ}
\def\omega{ω}
\def\varsigma{ς}
\def\varrho{ϱ}
\def\vartheta{ϑ}

\def\Alpha{Α}
\def\Beta{Β}
\def\Gamma{Γ}
\def\Delta{Δ}
\def\Epsilon{Ε}
\def\Zeta{Ζ}
\def\Eta{Η}
\def\Theta{Θ}
\def\Iota{Ι}
\def\Kappa{Κ}
\def\Lambda{Λ}
\def\Mu{Μ}
\def\Nu{Ν}
\def\Xi{Ξ}
%\def\Ο{O}
\def\Pi{Π}
\def\Rho{Ρ}
\def\Sigma{Σ}
\def\Tau{Τ}
\def\Upsilon{Υ}
\def\Phi{Φ}
\def\Chi{Χ}
\def\Psi{Ψ}
\def\Omega{Ω}

\begin{document}
\selectlanguage{english}

English text


$$α=\frac{β}{γ_s \text{ or }\oldgamma_s} \text{ or }\alpha=\frac{\beta}{\gamma_\sigma} \text{ and } 6_p$$


\selectlanguage{greek}

Ελληνικό κείμενο εδώ

$$α=\frac{β}{γ_s \text{ or }\oldgamma_s} \text{ or }\alpha=\frac{\beta}{\gamma_\sigma} \text{ and } 6_p$$

\setmainfont{FreeSans}
\selectlanguage{english}

English text


$$α=\frac{β}{γ_s \text{ or }\oldgamma_s} \text{ or }\alpha=\frac{\beta}{\gamma_\sigma} \text{ and } 6_p$$

\selectlanguage{greek}

Ελληνικό κείμενο εδώ

$$α=\frac{β}{γ_s \text{ or }\oldgamma_s} \text{ or }\alpha=\frac{\beta}{\gamma_\sigma} \text{ and } 6_p$$

\end{document}

Output:

PS: The package MnSymbol didn't used here and see the correction on the \oldgamma spacing.

Answer 2

Reading the question as 'How to use the same Greek font for maths and text', here is a unicode-math package way, with its granularity of approach: use the range= option to read in glyphs for one or more of the desired lowercase and uppercase Greek alphabets in the Mathematical Alphanumeric Symbols unicode block (bold, italic, bold-italic, sans bold, sans bold-italic).

It does give a more consistent look:

Direct input is also accepted (e.g., the red capital mu).

This example also sets Greek letter math-style to ISO style, rather than French or English. The maths font is XITS Math having its italic Greek and bold-italic Greek math alphabets replaced by the glyphs from the non-math Noto Serif italic and bold-italic faces, with Noto Serif itself being used for the Greek text font as well.

MWE

\documentclass[12pt,varwidth,border=6pt]{standalone}
%\usepackage{amsmath}
\usepackage{xcolor}
\usepackage{polyglossia}
\usepackage[math-style=ISO]{unicode-math}
\setmathfont{XITS Math}
%\setmathfont{Noto Serif}[range={up/{greek,Greek},it/{greek,Greek},bfit/{greek,Greek}},Colour=blue]%fontface; regular
\setmathfont{Noto Serif Italic}[range=it/{greek,Greek},Colour=blue]
\setmathfont{Noto Serif Bold Italic}[range=bfit/{greek,Greek},Colour=red]
\setmainfont{Noto Serif}
\setdefaultlanguage{english}
\setotherlanguage{greek}
\newfontfamily\greekfont[Script=Greek]{Noto Serif}

\begin{document}
\begin{greek}
Το \textbf{ηλιακό σύστημα} περιλαμβάνει τον Ήλιο και όλα τα αντικείμενα τα οποία κινούνται σε τροχιά γύρω από αυτόν μέσα στο πεδίο βαρύτητάς του, είτε περιστρεφόμενα άμεσα γύρω από αυτόν είτε κινούμενα σε τροχιές γύρω από άλλα σώματα που κινούνται γύρω από τον Ήλιο. Βρίσκεται στο τοπικό διαστρικό Νέφος, το οποίο ανήκει στην Τοπική Φυσαλίδα, η οποία με τη σειρά της ανήκει στον βραχίονα του Ωρίωνα στο Γαλαξία, σε απόσταση 27.000 ετών φωτός από το κέντρο του. -- \textit{Βικιπαίδεια}
\end{greek}

\[ \alpha^2 + \beta^2 = \gamma^2 \]

\[\Alpha_1 \Beta_1 = 4\Gamma_2 \]

\[ _{\iota} = (_{\alpha}, _{\beta}, _{\gamma})\cdot 4\sin^{2}()\]

\[α=\frac{β}{γ_s \text{ or }\gamma_s} \text{ or }\alpha=\frac{\beta}{\gamma_\sigma} \text{ and } 6_p\]
\ 
\end{document}

Unrelated: polyglossia, mathspec and unicode-math all use fontspec in the background.